1. Field of the Invention
The present invention relates to a method for boring dental radicular canals by means of a set of instruments which are successively passed through the said canals.
The invention also relates to a set of instruments for carrying out the method in which each instrument comprises a tapered stem provided, on at least a part of its length which constitutes its active portion, at least one helicoidal cutting edge. This stem presents a conicity, the angle or opening of which is higher, at its rear end, than the angle at its front end.
2. Description of the Prior Art
The boring of dental radicular canals comprises a first step called catheterization, which consists in engaging into the radicular canal a very fine instrument, up to the apical foramen. This operation is always performed manually.
The widening of the radicular canal is effected by several operations which can be performed either manually or by means of instruments mechanically driven. For this second step, two methods can be used: The first one, called "step back" consists of introducing into the canal a succession of instruments, the diameters of which are successively increasing, while reducing the part of the length of the canal which is bored at each application of an instrument having increasing diameter. This method is relatively long and does not permit the dentist to observe, so far as it is possible, the work which has been effected. The second method, called "crown-down", consists of opening, in a first step, the coronary portion of the tooth, then to enter, by means of a set of instruments which successively increase in fineness up to the apical zone of the tooth.
The known sets of instruments permitting carrying out of these methods are usually mounted in a hand-piece rotating slowly (250 to 500 t/min.); they are formed, in most of the cases, of a nickel-titanium alloy, and belong to three families:
The first family comprises a set of instruments formed of a short cutting portion, followed by a thin and flexible collet which is itself connected to a handle which is secured to a hand-piece to enable mechanical driving of the instrument. The diameter of the active portion of the instrument increases according to an arithmetic progression, the interval between two numbers of the instruments of the set being of 0.025 mm.
A second family comprises instruments the active portion of which, of a length of 16 mm, has a conicity of 0.04 mm per millimeter of length. This active portion is immediately followed by a cylindrical portion to permit connection with the handle of the instrument. The progression of the diameter at the point of the end of the active portion of the instrument is of 29% between each number of the instruments of the set.
Finally, a last family comprises instruments having an active length of 16 mm and presenting a conical envelope, all of these instruments having the same diameter at their end. Their conicity increases 0.05 mm for each number of the instruments of the set.